Surfactant-free colloidal strategies for highly dispersed and active supported IrO2 catalysts: Synthesis and performance evaluation for the oxygen evolution reaction

• We synthesize surfactant-free Ir nanoparticles in different solvents. • We compare the performance of OER catalysts made from these colloids. • We demonstrate that high dispersion can be reached in a wide range of metal loadings. • We show that for reaching such high dispersion, the colloidal stability of the nanoparticles as well as the support in the respective solvent is key. Water electrolysis is a pivotal technology to drive the energy transition towards a system based on renewable resources. The scarce Ir is a crucial element for the synthesis of heterogeneous catalysts for the oxygen evolution reaction (OER). Carbon supported Ir oxide catalysts obtained from surfactant-free colloidal Ir nanoparticles (NPs) synthesized in alkaline methanol (MeOH), ethanol (EtOH), and ethylene glycol (EG) are investigated and compared. The comparison of independent techniques such as transition electron microscopy (TEM), small angle X-ray scattering (SAXS), and electrochemistry allows shedding light on the parameters that affect the dispersion of the active phase as well as the initial catalytic activity. The colloidal dispersions obtained are suitable to develop supported OER catalysts with little NP agglomeration on a carbon support. Due to the high dispersion of the active phase, initial catalytic activities of more than 400 A g −1 Ir are reached at 1.5 V RHE when using carbon as a model support. While the more common surfactant-free alkaline EG synthesis requires flocculation and re-dispersion leading to Ir loss, the main difference between methanol and ethanol as solvent is related to the dispersibility of the support material. The choice of the suitable monoalcohol determines the maximum achieved Ir loading on the support without detrimental particle agglomeration. This simple consideration on catalyst design can readily assist the implementation of more relevant support materials for technical applications and significantly improved catalysts.